Power manager for an electrical power generator

ABSTRACT

An electrical power generator includes a controller for making a full power capacity of the generator available for consumption by at least one intelligent load coupled to an output of the generator. The controller obtains data from which both a present output power of the generator and a power capacity of the generator can be determined. The controller then provides the intelligent load with data indicative of both the present output power and the power capacity of the generator for use by the load in controlling its power consumption.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of application Ser. No. 11/156,216,filed Jun. 17, 2005 and entitled “Power Manager for an Electrical PowerGenerator” by Wei Wei Qi, Michael Rubbo and Richard Wainwright.

Reference is hereby made to U.S. Pat. No. 7,272,514 entitled “ProtectionSystem for an Electrical Power Generator” of Wei Wei Qi, Michael Rubbo,and Richard Wainwright. This application is hereby incorporated byreference as set forth fully herein.

BACKGROUND

The present invention relates generally to electrical power generationsystems, and more particularly to an electrical power generator havingself-monitoring capabilities that cooperate with at least oneintelligent load to safely utilize traditionally untapped powergenerating capabilities of the generator.

Electrical generators are used in a wide variety of dedicated electricalsystem applications and locations that require power independent of astandard electrical grid. Commonly, electrical generators are theprimary, if not only, source of electrical power on a vehicle or ship,or in a remote location such as on an oil platform, in a small town, onan island or along a pipeline. Electrical generators are also commonlyused as a backup power source in locations operating primarily off thestandard electrical grid.

Because of this primary role served by electrical generators, it isoften desired to keep the generator fully functioning, or at leastpartially functioning, in all circumstances. Maintaining the generatorat full capacity is complicated by the fact that the conventionalgenerator is a slave to its loads, the maximum sum of which may greatlyexceed a rated capacity of the generator. The generator itself cannotdirectly control its outputted power; it can only control its own outputvoltage. Rather, it is the generator's loads that control the draw ofpower from the generator. Thus, to avoid overloading conditions that mayharm the generator, the conventional generator simply shuts itself offupon detection of overloading condition indicators, such as excessivetemperature.

Generators typically have a rated continuous capacity that is determinedas the maximum quantity of power the generator can produce for anindefinite amount of time without risking damage to the generator.Generators also have a rated surge capacity determined as a value thegenerator can sustain for a limited time, such as when the generatorexperiences a surge in power demands due to the transitioning of thegenerator's loads between on and off states.

The rated continuous and surge capacities are typically veryconservative estimates of what the generator can actually handle. Thatis, most conventional generators can produce much more power than theirratings allow, and in use, much of the generator's power generatingcapacity is neglected. Nonetheless, to ensure their continuousoperation, generators typically are selected to have a sufficientcontinuous capacity rating to handle all loads operating simultaneouslyat full capacity. This assumption often results in the selection of alarger capacity generator than what may otherwise be required or theaddition of a second generator to allow a reduction in the load attachedto the first generator. In many situations, however, these solutions arenot appropriate due to cost, weight, size, and efficiencyconsiderations. Thus, there exists a need for a generator capable ofutilizing more of its capacity.

SUMMARY

The present invention is a system and a method for making a full powercapacity of an electrical power generator available for consumption byat least one intelligent load coupled to an output of the generator. Inaccord with the present invention, data is obtained from which both apresent output power of the generator and a power capacity of thegenerator can be determined. Data indicative of both present outputpower and the power capacity of the generator are provided to theintelligent load for use by the load in determining its powerconsumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of two power time relationships of a typical generatorfor illustrating a full power generating capacity of the generator.

FIG. 2 is block diagram of an electrical system in accord with thepresent invention.

DETAILED DESCRIPTION

The present invention is a generator that incorporates a powermanagement system that, in contrast to prior art generators that simplylimit the generator to its rated capacity, seeks to capture and utilizethe full power capacity of a generator. FIG. 1 is a graph illustratingpower-time relationships 6 and 8 of a typical generator for illustratingthis full capacity of the generator. FIG. 1 plots a quantity of powerproduced by a generator as a function of time that the generator cansustain production of that quantity of power without risking damage toitself given existing system parameters of the generator, such as anambient temperature, a temperature of various components of thegenerator, a rotational speed of the generator, and a frequency of thegenerator output. As the system parameters change, so too does thecapacity of the generator. For example, as the generator's ambienttemperature increases, the power capacity of the generator decreases.Thus, power-time relationships 6 and 8 shown in FIG. 1 exist fordifferent system parameters, with power-time relationship 6 illustratinga capacity of the generator for a first set of system parameters (e.g.,a low ambient temperature) and power-time relationship 8 illustratingthe generator's capacity for a second set of system parameters (e.g., ahigh ambient temperature).

As shown in FIG. 1, the typical generator can produce a relatively highquantity of power; however, it can sustain this quantity for only a veryshort period of time. As the produced quantity of power decreases, thelength of time that the generator can sustain this production increases.Eventually, the sustainable power levels off at a steady state value.

A rated continuous capacity and a rated surge capacity of a conventionalgenerator are generally conservatively drawn from these power-timecharacteristics of the generator. That is, these rated values aretypically determined from the generator's power-time relationshipcorresponding to a worse case scenario. The rated continuous capacity isgenerally determined as the steady-state value of the worse casescenario power-time relationship, while the rated surge capacity isdetermined as a multiple of the continuous capacity. The rated surgecapacity may in fact be less than the actual maximum power the generatorcan produce.

The present invention enables the generator to produce power over itsfull range of capacities, rather than simply limiting the generator toits rated continuous capacity. FIG. 2 is a block diagram of electricalsystem 10 in accord with the present invention. Electrical system 10includes electrical power generator 12 for supplying power to any of aplurality of different types of loads. For illustrative purposes only,generator 12 is shown in FIG. 2 with three loads 14, 16, and 18.

As shown in FIG. 2, generator 12 is a brushless generator that convertsthe rotational energy generated by prime mover 19 into a multiphasealternating current (AC). The present invention, however, is not limitedto only brushless generators, and other types of generators may besubstituted for brushless generator 12. As is conventionally known,brushless generator 12 includes voltage regulator 20 (or controller orprocessor), an exciter having stator field windings 22 and rotor fieldwindings 24, rotating rectifier 25, and a main generator having rotorfield windings 26 and stator field windings 28. Exciter rotor fieldwindings 24, rotating rectifier 25, and main generator field windings 26share a rotor and are separated by an air gap from the stator havingexciter stator field windings 22 and main generator stator fieldwindings 28.

The conventional power generating operations of generator 12 are wellknown. In operation, voltage regulator 20 receives a direct current (DC)voltage from battery 30. Alternatively, battery 30 could be replacedwith a permanent magnet generator or another source of DC voltage.Voltage regulator 20 supplies a first DC voltage to exciter stator fieldwindings 22, which in turn develop a magnetic field. Exciter rotor fieldwindings 24 are rotated in this magnetic field to produce a firstmultiphase AC voltage. The first AC voltage is then supplied to rotatingrectifier 25, which rectifies the first AC voltage into a second DCvoltage for supply to main generator rotor field windings 26. Thecurrent in main generator rotor field windings then generates a magneticfield which in turn produces a induces a multiphase AC power at anoutput of main generator stator windings 28. This AC power is suppliedto loads 14, 16, and 18 of generator 12, and also as feedback to voltageregulator 20.

Voltage regulator 20 uses this feedback to help maintain a constantvoltage at the output of generator 12, which may otherwise vary due tofactors such as a variable rotational speed of the rotor of generator12. Voltage regulator 20 accomplishes this goal by measuring the outputvoltage of generator 12 and adjusting a current provided to exciterstator windings 22 as needed in a closed-loop fashion.

Generator 12 improves upon conventional generators by adding powermanagement logic and communication abilities that allow for the captureand utilization of the full power generating capacity of generator 12.As will be more fully described below, the present invention essentiallyadds capabilities to generator 12 to monitor its own power productionand various other system parameters and to determine therefrom itspresent power generating capacity. In other words, the present inventionprovides intelligence to generator 12 to enable it to determine answersto the questions: “What am I presently doing?” and “What am I capable ofdoing?” This information is then communicated to at least oneintelligent load, which can adjust its consumption based upon thecapabilities of generator 12. Thus, electrical system 10 is afforded theopportunity make use of traditionally untapped power capabilities ofgenerator 12. In the embodiment of FIG. 2, these abilities are added tovoltage regulator 20, but in alternative embodiments, a separatecontroller may be added to implement these features.

As described above with reference to FIG. 1, the power generatingcapacity of generator 12 (i.e., what it can do) is directly affected bythe system parameters of generator 12 (i.e., what it is presentlydoing). For this reason, an important aspect of the present invention isthe ability of generator 12 to be aware of its own system parameters.Accordingly, generator 12 includes system sensors 32 for sensing and/ormeasuring a plurality of system parameters related to the operation ofgenerator 12, such as its ambient temperature, the temperature of itsstator, the temperature of its rotor, the power produced by its exciter,the rotational speed of its rotor, or the frequency of its outputsignal. System sensors 32 may include hardware and/or software that maybe contained in a single or multiple devices for sensing, measuring, orotherwise determining these various system parameters. Further, systemsensors 32 may be implemented in any of a plurality of conventionalmethods. Data indicative of these system parameters is then supplied tovoltage regulator 20. Thus system sensors 32 include hardware and/orsoftware for determining the voltage provided at, and the current drawnfrom, the output terminal.

Importantly, these system parameters also include the voltage suppliedat the output terminal of generator 12 and the current drawn from theoutput terminal of generator 12. From these two values, voltageregulator 20 can compute a proxy for the present output power as theproduct of the voltage supplied at the output of generator 12 and thecurrent drawn from the output of generator 12. While this value does notequal the actual power supplied by generator 12, it does serve as a fairrepresentation of the power supplied. Thus system sensors 32 includehardware and/or software for determining the voltage provided at, andthe current drawn from, the output terminal.

Another system parameter that voltage regulator 20 may includeinformation about is the amount of time generator 12 has been operatingat a particular output power. As described above, high power outputs canbe sustained for a limited time period. Thus, generator 12 may includehardware and/or software for monitoring the length of time generator 12has supplied a power outside the rated continuous capacity of generator12.

Voltage regulator 20 evaluates the present output power proxy and theremaining system parameters to determine a present operating point ofgenerator 12. In other words, voltage regulator 20 effectivelydetermines which power-time curve is the appropriate curve, and where onthat curve it is. From this information, voltage regulator 20 candetermine the present power capacity of generator 12. This powercapacity is the maximum power generator 12 can produce based upon thedata indicative of output voltage, output current, and system parametersof generator 12. The power capacity of generator 12 may be greater than,less than, or the same as the present power being supplied; butimportantly, it may exceed the rated capabilities of generator 12. Forexample, generator 12 will be able to produce more power on a cold daywith prime mover 19 operating at high speeds than on a hot day withprime mover 19 operating at a low speed.

A further aspect of the present invention is use of intelligent loads(i.e., loads having their own controller for controlling their own powerconsumption) communicatively connected to voltage regular 20 overcommunications network 44. As shown in FIG. 2, generator 12 providespower to loads 14, 16, and 18. Here, load 14 is a conventional “dumb”load, that is, a load with no intelligence associated therewith.However, loads 16 and 18 are “intelligent loads” in that both includetheir own controller for controlling distribution of power to their ownloads. In particular, load 16 includes load controller 34 and its ownload 36, while load 18 includes load controller 38 and its own loads 40and 42. Load controllers 34 and 38 are each communicably coupled witheach other and with voltage regulator 20 of generator 12 viacommunications network 44. By providing intelligence to both generator12 and loads 16 and 18, and communicably connecting each of the devicestogether via communications network 44, the present invention allows forimproved distribution of power.

Communications network 44 may be implemented with any communicationsprotocol. For example, communications network 44 may be implemented witha controller area network (CAN), which is one of the ISO standardcommunications protocols.

Load controllers 34 and 38 receive and convert power delivered to loads16 and 18 into useful forms for their associated loads. Load controllers34 and 38 further receive and evaluate the present output power proxyand the power capacity of generator 12 to determine whether to adjustthe power consumption of a respective one of loads 16 and 18. Loadcontrollers 34 and 38 of loads 16 and 18 each have a performance setpoint to which they strive. Load controller 34 and 38 further includesensors (not shown in FIG. 2) for measuring an actual performance ofloads 16 and 18. By evaluating how much work it has yet to do to achieveits set point, the quantity of power that generator 12 is presentlysupplying, and the quantity of power available to it from generator 12,load controllers 34 and 38 can make an intelligent decision about howmuch power to consume.

For example, load 18 would constitute a large load if it were avehicular air conditioning system in which load 40 is a compressor motorand load 42 is a compressor fan motor. In this example, the airconditioning controller (load controller 38) can evaluate both aquantity of power that generator 12 can supply and how the airconditioning system (load 18) is performing to determine whether toadjust its consumption. Thus, when the air conditioning system (load 18)is initially turned on to cool a hot space, and where generator 12 hasexcess capacity (that is, its power capacity exceeds its present powerproduction), air conditioning controller (load controller 38) may preferto operate the air conditioning system (load 18) at a higher consumptionrate until its set point has been met or until generator 12 reduces itscapacity. If generator 12 is operating above its capacity (the powercapacity is less that its present power production), the airconditioning control (load controller 38) may choose to decrease itspower consumption. Thus, rather than running continuously at lowersettings, air conditioning system (load 18) may perform its job faster,taking advantage of the additional operating envelope of generator 12for a period of time.

Load controllers 38 and 34 may also compute their own power consumptionby including sensors to measure input voltages to loads 16 and 18 andcurrents drawn by loads 16 and 18. As with generator 12, loadcontrollers 38 and 34 may compute and rely upon a proxy for the actualpower consumed, such as voltage consumed multiplied by current drawn. Byknowing their own consumption, load controllers 34 and 38 can evaluatetheir own operating point to determine their own capacity. Thus, muchlike generator 12 can operate over its rated continuous capacity,intelligent loads 16 and 18 may be able to operate over their ratedcontinuous consumption levels. This is an improvement over prior artload controllers which evaluate only temperature or current, and shutoff the device when either exceeds a predetermined limit. Anotheradvantage to evaluating power consumption is that load controllers 34and 38 can compare the actual power consumption to estimated powerconsumption for identification of component wear out, requiredmaintenance, or imminent failure.

Loads 16 and 18 are prioritized within system 10 to prevent each ofintelligent loads 16 and 18 from simultaneously grabbing excess powerfrom generator 12 upon generator 12 announcing (broadcasting) itsincreased capacity. Thus, the load with the lower priority will not havean opportunity to increase its consumption until after the load with ahigher priority makes its decision to adjust its consumption.

Load controllers 38 and 34 may also communicate their power consumptionproxy with each other and with generator 12 over communication network44 to allow for a more intelligent distribution of power. In this way,each of generator 12 and intelligent loads 16 and 18 can act in the bestinterest of electrical system 10, rather than operating in a vacuumwhere each is concerned only about its own performance. Suchcommunication may also allow for dynamic assignment of load priorities.For instance, if load 16 is assigned a higher priority and is closer toachieving its set point than load 18, generator 12 may reassignpriorities to result in an improved system performance.

By enabling load controllers 38 and 34 to communicate with voltageregulator 20, load controllers 38 and 34 can make requests of voltageregulator 20 to adjust the power provided to it. For example, if loadcontroller 38 realizes that load 16 could use additional power to bestmeet its set point, but also aware that load 16 cannot tolerate anyincrease in current, load controller 38 may broadcast a request tovoltage regulator 20 of generator 12 to “trim,” or temporarily increase,its output voltage—the resultant effect being an increase in powerwithout an increase in current.

Electrical system 10 can further be improved by adding “intelligence”,or a controller, to prime mover 19 which causes rotation of the rotor ofgenerator 12. This can be helpful in allowing prime mover 19 to controlthe electrical power generation load on it when needed. For instance,where prime mover 19 is an engine in a vehicle, and the vehicle isrequired to accelerate, as when the vehicle is attempting to pass intraffic or climb a hill, prime mover 19 can communicate a request tovoltage regulator 20 of generator 12 to reduce power consumption.Voltage regulator 20 can respond to this request by reducing the outputvoltage of generator 12, thus reducing its generated power and its loadon prime mover 19. Alternatively, prime mover 19 may request that thepower generated by generator 12 be diverted from electrical system 10 toan alternative system of loads, such as a transmission system of thevehicle.

Voltage regulator 20 cannot control consumption by its loads. Ifintelligent loads 16 and 18 do not respond to requests by voltageregulator 20 to reduce their consumption, voltage regulator 20 can forcea reduced power by lowering its output voltage. Because power is theproduct of the output voltage and the output current, this actionresults in a reduction in the power produced by generator 12.

In sum, the present invention is an electrical power generator thatmakes its full power capacity available for consumption by at least oneintelligent load coupled to its output. The generator includesself-monitoring abilities that enable it to determine a present outputpower of the generator (i.e., what it is presently doing) and, fromthat, a power capacity of the generator (i.e., what it can do). Thesevalues are then broadcast to the intelligent loads via a communicationsnetwork for use by the intelligent loads in controlling their ownconsumption.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. An electrical system comprising: a plurality of variable loads; anelectrical power generator that provides power to the variable loads viaan output terminal; a plurality of system sensors that sense a pluralityof generator parameters related to the operation of the generator, thegenerator parameters including a voltage at the output terminal of thegenerator and a current drawn from the output terminal of the generator;a generator controller that is coupled to the plurality of systemsensors for receipt of data indicative of the plurality of generatorparameters and that determines therefrom a present generator outputpower proxy and a generator power capacity; and at least one loadcontroller that is communicably coupled to the generator controller forreceipt of data indicative of the present generator output power proxyand the generator power capacity and that controls a power consumptionof at least one of the variable loads as a function the presentgenerator output power proxy and the generator power capacity.
 2. Theelectrical system of claim 1 wherein the generator parameters furthercomprise at least one parameter selected from the group consisting ofambient temperature, stator temperature, rotor temperature, rotor speed,and output signal frequency.
 3. The electrical system of claim 1 whereinthe generator parameters further comprise an amount of time thegenerator has been caused to operate outside of its rated continuouscapacity.
 4. The electrical system of claim 1 wherein the at least oneload controller comprises a plurality of load controllers communicablycoupled to each other and to the generator controller via acommunications network.
 5. The electrical system of claim 4 wherein eachload controller evaluates a performance set point of its load, ameasured performance of its load, a present power consumed proxy of itsload, a power consumption capacity of its load, the present generatoroutput power proxy, and the generator power capacity in determining thepower consumption of its load.
 6. The electrical system of claim 5wherein each load controller communicates the present power consumptionof its load and the power consumption capacity of its load to both theother load controllers and the generator controller via thecommunications network.
 7. The electrical system of claim 4 wherein thegenerator controller is responsive to a request from one of the loadcontrollers to adjust the output voltage of the generator.
 8. Theelectrical system of claim 4 wherein the load controllers have priorityvalues associated therewith for determining an order in which the loadcontrollers determine the power consumption of their load.
 9. Theelectrical system of claim 1 and further comprising: a prime mover thatprovides a rotational energy to the generator for conversion by thegenerator into electrical power; and a prime mover controller thatcontrols a rotation of the prime mover and that is communicably coupledto the generator controller via a communications network, wherein thegenerator controller is responsive to requests from the prime movercontroller to adjust a power generation load of the generator on theprime mover.